Bereshit B: Chapter 51
Voice and speech

A deeply hidden secret pertains to the spiritual powers of the mouth. As letters and words arouse the very forces that they describe, the mouth animates the spiritual forces that it speaks. Positive words generate positive angels, while negative speech produces negative angels. The good and bad events in our lives are merely the net effect of the angelic influences created through the power of speech. The Evil Inclination works to blind us from this spiritual truth. Having succumbed to the uncertainty and doubt implanted within us by our negative tendencies, most of us disregard the words that come out of our mouths. Yet Kabbalah teaches that it is far more important to consider what comes out of the mouth than what goes into it. It is fitting that, through the power of the Zohar's words, we can draw Light to help us use our speech in a positive manner.